One of the setups I had come to imagine was a workshop machine (AM2 or similar) with three fluid interfaces in different directions, and one item interface direction in the fourth direction. If the recipe is not set, the fluid interface will be visible in absolutely no manner, and it becomes frustrating guesswork to figure out how to rotate the machine before setting the recipe. I can also see similar frustration if someone plunks down a chemical plant or refinery and the pipes leading up to or from it are backwards. Not being able to set the recipe would make it far harder to troubleshoot such a problem than it currently is - at least for inputs. A new player might even mistake this behaviour for a game breaking glitch and throw Factorio out in frustration.

You would not be able to rotate it back. Any such action attempt will give you a warning about the fluid mixing, so anyone should be able to figure it out. Even if it ends up confusing for somebody, it is still less confusing then the result would be previously.

With this behaviour, the only way I see solving the problem I left in from my previous post is by breaking all the pipes adjacent to the machine to be able to rotate it or diagnose issues, which is far from ideal. I'm actually quite certain it would behave better than you describe in the current game where an AM2+ only consumes fluid, but I haven't set anything like this up in anger (so to speak) because mixing fluid networks is that much of a disaster that I'm quite paranoid about it. I think I can slap together a test setup when I have more time to play; I certainly wouldn't take the risk in any "real" games.

I really like this. Would be weird if I didn't considering I also suggested this very exact thing(The using unmodified data from the previous tick to calculate flowrates and then moving the fluid to avoid update order dependant behaviour. And by the way this is completely parallelizable down to individual fluidboxes since all threads only read "static data" from the last tick) back in March 2017. I even suggested a pingpong design wich is basically having two variables for the fluid amounts and switching wich one to read and write so you don't have to copy the values to temporary variables costing a bit more memory but saving some cpu cylcles.

I don't know if you(Dominik) were around back then and the thread died pretty quickly so I won't blame you for not knowing or paying attention to it. Granted I didn't have a simulator or that much code or anything really to back up the idea and back then the fluid mechanics didn't seem like a high priority. Maybe if the thread had gone for longer.

And even I will admit that it wasn't an original idea but a solution that I had to study for extra credit at school for simulating fluids almost 10 years ago. Back then my friend and I used it to simulate waves on a lake. I don't really remember the names of the papers I read back then about the subject but they were from the 90's. And I'm sure there are plenty of others who have talked about this thing or something similar before on the forums maybe even before the thread I linked.

But thanks @TheYeast for doing all the amazing work with the simulator and working out the math and such and finally selling(I hope not literally) the idea to you. Can't wait for it to actually getting to the public version.

Oh and just to be clear I did not make this post to claim any credit or discredit anyone else so please don't hate me. I just wanted to explain why I personally very much agree to this idea.

I'm so excited about this new fluid system. More intuitive, CPU friendly, isotrope, and above all faster fluid flow. This will allow to use medium sized oil and nuclear setups without spamming pumps as much as before!

@Dominik, With this new viscosity, can I expect crude oil to be roughtly as fast as before (or a bit slower), water a bit faster, and gas (petroleum and steam) much faster?

By the way, I think fluid separation is obviously a good thing. And as it seems like fluid mixing will still be possible with use of fluid pumps connecting (or not) to fluid wagons, that would lead to overly complicated (and fun?) setups.
And hype for flow-rate toolbox and faster draining time with the 0.05 unit threshold.

Alright, with the fluids now behaving in a more reasonable manner, what are the actual limits? How far can we flow water from an offshore or regular pump at the maximum rate? This will be the real test of the new system, since power generation / water use frequently bottlenecked on the old system's flow capabilities...

I am sure this new system is better than the old system as pretty much anything would be better than the old system. But i also fear it's also going to be annoying.

Here's a few concerns of mine currently, which i hope can be fixed by the end user through modding at least.

Flow rate - There comes a point where one needs higher flow rates than what is available through a single piece of vanilla pipe. That is, no matter how many pumps one uses, even a single pipe will be a bottleneck.
In the old system one had to pretty much destroy viscosity of the fluid for it to flow. This because the old system was only dependant on pressure, not actual cross section (volume) of pipe. And you couldn't increase pressure in a sensible manner... In real life, oil trapped underground and suddenly released can shoot out at amazingly high pressures and flow rates. Despite the "pipe" it flows through being rather small.

Machines have massive limitations with pipes in the number of connections they have and where those connections are placed. Limitations that rarely exist for items.

In short, i really hope we can increase pressure and volume of pipe in such a way that getting fluids around hungry machines won't be an issue with this system.

Time to travel - You mention that fluid amounts < 0.05 will clear out automatically. Well, how fast will this happen? Is it faster than just removing all pipes manually and re-placing them? Again, in real life, pipes are cleaned by scrubbing and washing out the old gunk and takes forever. But factorio isn't real life, one doesn't want to wait.
In Factorio, it usually is enough to place a pump at some end going into a single fluid box to clear a pipe and the length of pipe it clears doesn't really matter as the speed in doing this is damn high anyways. And in the off chance that fluids don't flow (< 0.05 amounts whatever) you simply rotate the pump and try again until all moves in one go due to the flow bonus.

I find myself using the same pipes for different fluids currently depending on what i need at the time. Hence i empty often.

But if fluids emptying is a PITA in the new system i suspect people (me included) are going to fix the issue by modding and if not possible, go back to 0.16 and stay there until it's fixed.

Upgrading - You mention that using underground pipes won't help now. Well, that has been the only way to increase flow rate currently along with pumps every so often (in my case, pump->pipe->pump->pipe->pump) and this concerns me.
Again, in a real life situation you can always use a bigger pipe. In Factorio however, pipes are one tile wide and that's it. This because machines fluid ports are one tile wide.

So again, how would one be able to perform upgrades to the fluid network once they find that one single pipe is the bottleneck for the whole thing?
It's not as simple as just using two pipes side by side. Getting the fluid in and out of machines is still a massive problem in megafactories because of how pipes connect, how they don't exist neatly side by side (different fluids) and how they are "one size fits all".

I want to be able to use different pipe dimensions and different pipe materials for different applications. If i want extremely high flows i would go with a bigger cross section pipe made with an extremely strong material to be able to pressurize the system to high levels to increase flow rate even for highly viscous fluids.

But it's not all concerns of course, i am really glad that splitting flows has been dealt with now. No more intermediate storage tanks with pumps controlled to only pump when all extracting pumps have enough fluid for one tick of operation.
And i am sure the new system will allow for more options now.

I just hope it's not going to completely destroy the balance of the game just because someone wanted fluids to move "realistically" through pipes.

While finalizing it, ensure that extreme situations can still be addressed in modding and all is good.
Oh and it would be really nice if we could have some flags on fluids too. Such as "corrosive", which would require the use of a pipe material that can take corrosive fluids.
Or "gas", which requires stronger pipes to ensure gasses don't escape through the connections.
And even "max pressure" so if fluids go over that pressure in the system, the fluids would "escape" (not necessarily leak on the ground, that depends on mods that do such things) which would require the use of a stronger pipe.

EDIT: Mind you, i am really tired at the moment so i read the blog post in a dozy state and might not have understood the new system at all.

I don't know what you guys screwed up, but I'm noticing a distinct lack of complaints in the replies so it must be something HUGE.

The complainers are still fully occupied with the axe axing thread...

The new fluid logic is implementing The Yeast's model, wich brings exactly the right amount of realism into the game and is optimization friendly. So they really did the least controversial thing possible.
Modders gonna love the new customizability of fluids, megabasers like the UPS improvements, and regular players will not mix their fluids by accident anymore.

So there are only questions about other nice-to-haves, hoping that they implement them while tuning the fluid-mixing prevention logic - like removal of the need for gaps between pipes carrying different liquids and the ability to do circuit-less multi-fluid train stations.

P.S.: I also want the spidertron and a ranged boss biter scorpion (the latter would technically be easy to implement as a larger spitter with more damage output, but would need some artist time for making the new model).

I don't know what you guys screwed up, but I'm noticing a distinct lack of complaints in the replies so it must be something HUGE.

Just wait until the I-want-fluids-to-be-as-simple-as-electricity proponents get here...

I want the electricity system to be as detailed as the new fluid system! I do really want a more detailed electrical system but I understand why it is the way it is.

If you're interested in having a serious conversation on that topic, please meet me over at FFF#270 where my simple per pole loss factor proposal is somehow incomprehensible to just about everyone there.

Thank you devs!!! I'm really excited that Factorio is heading towards multi-threading I'm not sure, but will Factorio be one of the first big simulation games to use all 32 threadripper cores? I have the 16-core right now, so I'm excited!

If you're interested in having a serious conversation on that topic, please meet me over at FFF#270 where my simple per pole loss factor proposal is somehow incomprehensible to just about everyone there.

Actually I like this. No UPS cost, nerfs solar, forces you to think rather than just spam poles. Pretty good.

Sounds a bit like the infrastructure maintenance patch for OpenTTD. Putting a constant cost on static infrastructure, a simple change that adds so much to the game.

EDIT: I don't know anything about modding, but shouldn't this be possible to mod in by making power poles electricity consumers? So that we can test it.

How will this work with non-pipe fluidboxes, i.e. turbines or steam engines? For example, how will low temperature steam mix with high temperature one? Or they just won't? It's technically the same fluid and there were nuclear builds with adding additional steam engines at the end to utilize leftover steam, soooo.